The disclosed embodiments of the present invention relate to setting power of a wireless communication channel, and more particularly, to a power adaptation apparatus and power adaptation method for controlling uplink/downlink power.
Inner/outer loop power control is a well-known method of dedicated channel (DCH) power adaptation as specified in universal mobile telecommunications system (UMTS)—frequency-division duplexing (FDD) specification. FIG. 1 is a block diagram illustrating a conventional DCH uplink (UL) power control mechanism. The user equipment (UE) 102 communicates with the UMTS terrestrial radio access network (UTRAN) 104 via a radio interface 101. The UE 102 may include a UL power control block 112 and a demultiplexer (DEMUX) 114, where the UL power control block 112 is arranged to set the power of the UL physical channel, and the DEMUX 114 is arranged to output the transmit power control (TPC) command received from the downlink (DL) physical channel to the UL power control block 112 such that the UL power control block 112 would adjust the power of the UL physical channel in response to the TPC command. Regarding the UTRAN 104, it may include a signal-to-interference ratio (SIR) measurement and TPC decision block 122, a block error rate (BLER) measurement block 124, and a multiplexer (MUX) 126. The inner loop power control can be used to adaptively control the UL power in response to the radio quality variance. Thus, the SIR measurement and TPC decision block 122 is arranged to measure the radio quality (i.e., SIRest), and compares the measured radio quality with the desired radio quality (i.e., SIRtarget). When SIRest is found smaller than SIRtarget, implying that the actual radio quality is lower than the desired one, the SIR measurement and TPC decision block 122 generates an “UP” TPC command, and transmits the “UP” TPC command to the UE 102 through the MUX 126. Next, the UL power is increased by the UL power control block 112 due to the “UP” TPC command. When SIRest is found larger than SIRtarget, implying that the actual radio quality is higher than the desired one, the SIR measurement and TPC decision block 122 generates a “DOWN” TPC command. Next, the UL power is decreased by the UL power control block 112 due to the “DOWN” TPC command. In this way, the radio quality is adapted by the inner power control which adjusts power of the UL dedicated physical control channel (DPCCH) and dedicated physical data channel (DPDCH) based on SIRest and SIRtarget.
SIRtarget is an estimated SIR for achieving a target BLER of DCH. For example, the target BLER can be 10%. However, the value of SIRtarget may be out-of-date because radio condition is always changing. Thus, the outer loop power control can be used to update SIRtarget once the currently used SIRtarget is no longer proper. Therefore, the BLER measurement block 124 is used to obtain a measured BLER of DCH, and then increase or decrease SIRtarget according to the measured BLER.
To increase the uplink data rate, throughput and capacity, high speed uplink packet access (HSUPA) is therefore developed. Within the HSUPA framework, the enhanced dedicated channel (E-DCH) is introduced as a new transport channel for carrying user data on the uplink. On the physical layer level, the E-DCH includes two uplink channels, an E-DCH dedicated physical control channel (E-DPCCH) and an E-DCH dedicated physical data channel (E-DPDCH). Based on the HSUPA specification, the power of E-DPCCH and E-DPDCH of E-DCH is directly set in relation to power of DPCCH. For example, in accordance with the conventional design, the power of DPCCH is controlled according to the inner loop power control and outer loop power control shown in FIG. 1. However, there is no mechanism available to adapt the E-DCH BLER. In other words, SIRtarget cannot be updated even if the radio condition of E-DCH has changed. Hence, SIRtarget would be out-of-date for E-DCH, and the originally expected E-DCH BLER cannot be achieved. As a result, the HSUPA uplink transmission throughput/performance may be corrupted in a high-interference radio condition. Besides, the HSUPA uplink transmission power may be over-estimated to make an unreasonable low E-DCH BLER in a low-interference radio condition. To put it simply, the original target E-DCH BLER may become unreachable when the radio condition is variant. Thus, regarding the HSUPA transmission case, there is a need for an innovative power adaptation design to improve transmission performance in variant radio conditions.